Genetically and physically male babies born with a rare condition called "micropenis" are happier when raised as boys, according to research.

Those born with micropenis and raised as girls said they identified solidly with their female gender, but only 20% of the women said they were satisfied with their genitalia.

However, 50% of men, some of whom had achieved normal penis length with the help of testosterone replacement, said they were satisfied with their genitalia.

Raising a baby either male or female presents parents with challenges

Dr Amy Wisiewski

An article in Hormone Research says parents often choose to have their child brought up female because micropenis can sometimes result in inadequate male sexual function later in life.

Psychologist Amy Wisniewski, who led the US-research, said: "Raising a baby either male or female presents parents with challenges.

"But we were pleased with the successful outcome of some of the males.

"All men who were compliant with their testosterone replacement attained a final penile length within the normal range."

Micropenis is when the penis elongates properly during the first trimester of pregnancy in a male baby, but fails to grow normally in the second and third trimesters.

Micropenises are typically 1.9cm or less at birth when stretched.

Child 'cruelty'

Micropenis may also be accompanied by small testes and lower testosterone production, which often leads to enlarged breasts and sparse body hair as the child grows older.

The research team collected birth and adult genitalia measurements from 13 men an 5 women, all born with a micropenis.

They surveyed the individuals, all adults between 21 and 54 years of age for self-assessments of gender identity, sexual function and satisfaction with their genitalia.

They also asked participants questions regarding sexual orientation, marriage and satisfaction with their sex of rearing.

Males responded well to testosterone

Of the 12 men who responded, 10 reported a male heterosexual orientation, six were married and 11 said they were satisfied with their sex of rearing.

Among the four women who responded, three reported a female heterosexual orientation, none was married, and all were satisfied with the sex of their rearing, although men were more often satisfied with the appearance of their genitalia.

Dr Wisniewski said: "Our recommendation that babies be raised male is based not on problems with gender identity but on the difficulties associated with the surgical construction of a vagina and subsequent hormone treatment."

The UK Intersex Association (UKIA) is not surprised by the results of the study.

Mairi MacDonald said: "The opinion of UKIA is that carrying out genital cosmetic surgery in an attempt to reassign an infant's gender identity from male to female on the sole grounds that he has a small penis would, in a sane world, be classed as child abuse.

"Those responsible would be prosecuted and banned from further practice in the field of paediatrics."